Orthopedic implants are used commonly as structural reinforcements in the human body. By way of example, orthopedic implants are used to strengthen failed bone (e.g., broken or deteriorating bone), to stiffen compromised vertebrae, or to eliminate painful arthritic or damaged joints. Most orthopedic implants presently in use involve the extensive use of permanent metal hardware, such as, for example, bone plates and screws and spine cages.
Despite the enhanced mechanical strength and stiffness associated with them, such traditional metallic orthopedic implants require invasive surgical techniques which impose a large degree of surgical trauma, suffering, and rehabilitation time on patients. As an example, the treatment of hip fractures often requires an incision that is twelve inches or longer. Furthermore, when a stiff metal plate or implant is attached to bone, it tends to “shield” the bone tissue from mechanical stresses, and, under these conditions, native bone undesirably tends to resorb away.
Nevertheless, finding suitable alternative biomaterials has proven to be difficult. Particularly, existing non-metal biomaterials have not been satisfactory, for example, because they are inadequate with respect to mechanical properties (e.g., strength). For example, dense ceramics would have similar problems because they are stiff, and, thus, are stress shielding, and they have the additional drawback of being brittle such that they have a lower fracture toughness. In addition, non-metal biomaterials, such as, for example, existing polymeric and porous ceramic biomaterials are significantly inferior to natural cortical bone in terms of mechanical properties, such as, for example, elastic modulus, tensile strength, and compressive strength.
By way of example, one alternative approach to the use of metals in the field of orthopedics involves minimally invasive orthopedic implant surgical techniques in which injectable bone glue and filler materials are used (e.g., to repair a bone fracture) instead of metal plates and screws and the like. As an example, the “skeletal replacement system” (SRS) offered by Norian Corporation (Cupertino Calif.) involves an injectable cementitious material that cures after injection in the body (i.e., in vivo). However, the SRS material has proven to be unsatisfactory for many load bearing applications because of its inferior tensile properties and low fracture toughness.
In addition, noteworthy among polymeric materials is the polymethyl methacrylate (PMMA) cement. The PMMA cement also suffers from insufficient mechanical properties, which, while generally better than SRS, are still inferior to those of natural cortical bone. In addition, another shortcoming associated with PMMA cement is that a large amount of heat is generated undesirably during the exothermic curing process. The heat generated during the exothermic curing reaction limits the volume of a bone defect that can be filled inasmuch as a large volume of bone cement will generate sufficient heat to kill adjacent tissues. Furthermore, PMMA cement also has a tendency to leach out MMA monomer that can have toxic effects on nearby tissues.
Accordingly, it will be appreciated from the foregoing that there exists a need in the art for a biomaterial (e.g., for orthopedic implants) with desirable biomechanical properties, as well as methods of preparing such biomaterials. It is an object of the present invention to provide such a biomaterial and related methods. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.